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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 34, Number 1
BKCSDE 34(1)
January 20, 2013 

Spectroscopic Properties of Flavonoids in Various Aqueous-Organic Solvent Mixtures
Hyoung-Ryun Park, Yu Daun, Jong Keun Park, Ki-Min Bark*
Flavonoids, Fluorescence spectroscopy, Intramolecular charge transfer, Intramolecular proton transfer
The characteristic fluorescence properties of quercetin (QCT) and apigenin (API) were studied in various CH3OH-H2O and CH3CN-H2O mixed solvents. The structure of QCT is completely planar. API is not planar at the ground state but becomes nearly planar at the excited state. If the molecules are excited to the S1 state in organic solvents, QCT exhibits no fluorescence due to excited state intramolecular proton transfer (ESIPT) between the -OH and the carbonyl oxygen, but API shows significant fluorescence because ESIPT occurs slowly. If the molecules are excited to the S2 state, both QCT and API exhibit strong S2 → So emission without any dual fluorescence. As the H2O composition of both solvents increases, the fluorescence intensity decreases rapidly due to the intermolecular hydrogen bonding interaction. The theoretical calculation further supports these results. The change in fluorescence properties as a function of the solvatochromic parameters was also studied.
211 - 220
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